Heat treatment of steel rails



Patented Aug. 29, 1933 HEAT TREATMENT OF STEEL RAILS John Brunner, Chicago, 111.

No Drawing. Application March 25, 1933 Serial No. 662,839

RUSSQEQ 4 Claims. (Cl. 148 12) This invention relates to improvements in the manufacture of steel rails and similar rolled shapes.

According to standard practice steel rails are rolled to a finished section and are then permitted to cool down to atmospheric temperature. The defect which has existed as a problem in this art is the occurrence of so-called shatter cracks forming in the interior of the rail .during the cooling after the rolling of the rail is completed. The existence of such shatter cracks may be determined by etching and by microscopic examination of a section taken longitudinally through the head of the rail. Such shatter cracks tend to enlarge and in service, may finally cause failure of the rail. Various methods have been resorted to in an attempt to prevent the occurrence of such shatter cracks but heretofore a cheap and efiicient method has not been disclosed.

In a former patent granted to me as No. 1,277,- 3'72, September 3, 1918, I have disclosed a method for finishing rails, having for its principal object the production of a fine grain structure in the interior of the rail head. According to this prior method the rail is rolled to a size slightly in excess of the finished rail. The rail is cooled to a temperature below the critical range, then reheated to a temperature above the critical range until the structure attains the fine grain and then the rail is rerolled to its finished section and allowed to cool on a hot bed. This former method was not directed to the preventation' of shatter cracks but to the formation of a fine grain structure.

It is an object of the present improvements to disclose a method according to which-a finished rail, having a fine grain structure with great toughness and without the existence of shatter cracks, may be obtained.

Specifically it is an object of the present invention to finish the rail by the following method: The rail is rolled to its finished section; cooled to a temperature below the thermal critical range; reheated to a temperature above the thermal critical range and then cooled, either naturally or by regulated cooling until it reaches atmospheric temperature.

The treatment herein described is applicable to rails having a composition substantially within the following ranges:

' Carbon between 0.20% and 0.90% Manganese between 0.30% and 1.60% Phosphorus not over 0.08%

Sulphur not over 0.08% Silicon not over 2.00% Chromium not over 3.00%

and other chemical elements may be added as de-oxidizers or strengtheners of the steel. It is to be understood that the chemical composition is to be adjusted to best suit the particular section of rail used and the intended service of the rail.

The rails leave the finishing rolls at a temperature approximately 925 C. to 1065 C. The rails are transferred to a hot bed and cooled either naturally or by regulated air cooling to a temperature just below the thermal critical range or temperature of recalescence. The exact temperature will vary in accordance with the chemical composition of the steel but it may be approximately stated as 500 C. to 700 C. The rails are then transferred to a reheating furnace, where the temperature is slowly raised to a point slightly above the upper limit of the thermal critical range which may be stated as approximately 800 to 850 C. The rails taken from the furnace are again transferred to a hot bed where they are cooled, either naturally or by regulated cooling, down to atmospheric temperature. The rate at which the cooling and reheating steps are carried out is variable, depending upon the composition of the rail, the section of the rail and weather conditions, but it may be understood that the period from the time the rails leave the finishing rolls until they finally reach approximately atmospheric temperature may require several hours.

By the treatment herein described I prevent the formation of so-called shatter cracks in the interior of the rail during the cooling by the re-. moval or equalizing of internal stresses and strains incident to the cooling operation and the treatment effects a refinement of the internal grain structure of the rail and increases the uniformity and toughness thereof. Furthermore, it is important to note that the treatment described is carried out on the finished rail so that no subsequent heating of the rail due to further rolling.

takes place. Therefore, there is no possibility of further changes in the grain structure or danger of formation of shatter cracks after the rails are treated as herein described.

This application is a continuation-in-part of application Serial No. 632,087, filed September 7, 1932, and is intended to correct an inadvertent error therein in stating the analysis of the rail steel composition.

I claim:

1. The method of treating steel rails which consists in rolling the rails to finished sections, cooling the rails from their rolling temperature to a point only slightly below the thermal critical range, reheating the rails to a point slightly above the thermal critical range and cooling the rails to atmospheric temperature.

2. The method of manufacturing steel rails which consists in rolling the rails to finished sections, cooling the rails from the rolling temperature to below the thermal critical range, reheat- C. and cooling the rails to atmospheric temperature.

4. The method of manufacturing steel rails which consists in rolling the rails to finished sections, cooling the rails from the rolling temperature to approximately 500 C., reheating the rails to approximately 850 C., and cooling the rails to atmospheric temperature.

JOHN BRUNNER. 

